The present invention relates to a device transfer method of transferring light emitting devices such as light emitting diodes, which have been formed on a substrate, for example, a sapphire substrate, to a device transfer body such as a display panel, and to a panel on which the transferred devices are arrayed.
A known method of producing an LED (Light Emitting Diode) display using LEDs includes the steps of cutting an LED wafer, which is obtained by stacking semiconductor layers on a device formation substrate, into chips by a diamond blade or the like, and transferring the LED chips to a display panel or the like with a pitch larger than an array pitch of the LED chips on the device formation substrate.
The above-described cutting method, however, has problems. For example, blue light emitting diodes are produced by stacking gallium nitride based semiconductor layers on a sapphire substrate as a device formation substrate. In this case, sapphire used as the material of the substrate is as very hard, about 9 in Mohs"" hardness. As a result, if the sapphire substrate is full cut into chips by a dicer such as a diamond blade, problems such as cracking and/or chipping tend to occur in the cut planes of the sapphire substrate which prevent the sapphire substrate from being smoothly cut into chips of desired shapes and sizes, the dicer itself may also be broken, and that since sapphire has no cleavage characteristic, it is difficult to cut the sapphire substrate into chips by forming scribing lines on the sapphire substrate and forcibly cutting the sapphire substrate along the scribing lines by an external force.
To solve the above problems, a method of cutting a sapphire substrate has been disclosed, for example, in Japanese Patent Laid-open No. Hei 5-315646. According to this method, as shown in FIG. 12, a gallium nitride semiconductor layer 61 formed on a sapphire substrate 60 is cut by a dicer to form grooves 62 deeper than a thickness of the gallium nitride semiconductor layer 61. The sapphire substrate 60 is thinned by polishing a back surface of the sapphire substrate 60. Scribing lines 63 are formed on the sapphire substrate 60 via the grooves 62 by a scriber. The sapphire substrate 60 is then forcibly cut into chips by an external force. This document describes how the sapphire substrate can be smoothly cut into chips without occurrence of cracking and/or chipping in the cut planes of the sapphire substrate 50. However, such a cutting method, requires several steps including the labor intensive step of polishing the sapphire substrate 60. In other words, the above method of cutting a sapphire substrate 60 is expensive and time consuming.
If a larger number of LED devices are obtained from one device formation substrate, the cost of one LED device can be reduced and the cost of a display unit using such LED devices can be also reduced. In the method disclosed in the above document, Japanese Patent Laid-open No. Hei 5-315646, LED devices each having a size of 350 m per side are obtained from the sapphire substrate having a diameter of two inches. If LED devices each having a size of several tens m per side are obtained from the sapphire substrate having a diameter of two inches and a display unit is produced by transferring the LED devices on a display panel, it is possible to reduce the cost of a display unit.
However, if the size of each LED device becomes as small as several tens of m per side, it becomes difficult to handle the LED device in the transfer step. Further, since an electrode of each device to be connected to a wiring layer of a base body of a display panel becomes small, the connection work becomes difficult and also a connection failure may often occur.
An object of the present invention is to provide a device transfer method capable of easily, smoothly separating devices from each other, and facilitating handling of devices in a transfer step and ensuring good electrical connection between the devices and external wiring, although the devices are fine devices, and to provide a panel on which the transferred devices are arrayed.
To achieve the above object, according to a first aspect of the present invention, a device transfer method is provided, the method includes covering a plurality of devices, formed on a substrate, with a layer of resin; the resin layer is then cut, to obtain resin buried devices each of which contains at least one of the devices. The resin buried devices are then peeled from the substrate and transferred to a device transfer body.
With this configuration, the resin buried device being handled has a size larger than the device itself The larger size of the resin buried device facilitates the handling of the devices in the transfer step. Since respective resin buried devices are obtained by cutting only the resin layer without the need of cutting the substrate, it is possible to easily obtain the resin buried devices because the resin layer can be easily, smoothly cut. Further, the substrate, which is not cut, can be reused.
According to a second aspect of the present invention, a device transfer method is provided which includes a step of covering a plurality of devices, which have been formed on a substrate, with a resin layer. Electrodes are formed in the resin layer in a manner such that the electrodes are connected to the devices. The method further includes cutting the resin layer to obtain resin buried devices, each containing at least one of the devices. The resin buried devices are then peeled from the substrate and transferred to a device transfer body.
With this configuration, the resin buried device being handled has a size larger than that of the device itself. The larger size of the resin buried device facilitates the handling of the devices in the transfer step. Since the electrode is formed in the resin layer in such a manner as to be connected to the device, it is possible to easily form the electrode, and to prevent connection failures between the electrode and an external electrode by increasing the area of the electrode. Since respective resin buried devices are obtained by cutting only the resin layer without the need of cutting the substrate, it is possible to easily obtain the resin buried devices because the resin layer can be easily, smoothly cut. Further, the substrate, which is not cut, can be reused.
According to a third aspect of the present invention, a device transfer method is provided which includes the step of covering a plurality of devices, which have been formed on a device formation substrate, with a first resin layer. The method further includes collectively peeling the devices, together with the first resin layer, from the device formation substrate, and transferring them to a first supporting board. Next, the first resin layer is cut on the first supporting board, to make the devices separable from each other. The devices covered with the first resin layer are then peeled from the first supporting board, and transferred to a second supporting board. The devices thus transferred to the second supporting board are then with a second resin layer. Electrodes are formed in the first and second resin layers in such a manner that the electrodes are connected to the devices. The method then involves cutting the second resin layer to obtain resin buried devices each containing at least one of the devices. The resin buried devices are peeled from the second supporting board, and transferred to a device transfer body.
With this configuration, the resin buried device being handled has a size larger than that of the device itself. The larger size of the resin buried device facilitates the handling of the devices in the transfer step. Since the electrode is formed in the first and second resin layers in such a manner as to be connected to the device, it is possible to easily form the electrode and to prevent occurrence of connection failures between the electrode and an external electrode by increasing the area of the electrode. Since respective resin buried devices are obtained by cutting only the first and second resin layers without the need of cutting the substrate, it is possible to easily obtain the resin buried devices because the first and second resin layers can be easily, smoothly cut. Further, the substrate, which is not cut, can be reused.
According to a fourth aspect of the present invention, a panel including an array of resin buried devices is provided. Resin buried device contains at least one device. A plurality of the devices are formed on a substrate and are covered with a resin layer. The resin layer is cut to obtain the resin buried devices each containing at least one of the devices. Furthermore, the resin buried devices are peeled from the substrate and are transferred to the panel.
With this configuration, it is possible to provide an inexpensive panel.
In the above device transfer method, preferably, connection holes are formed in the resin layer in a manner such as to reach the devices by laser beams, and the electrodes are connected to the devices via the connection holes. With this configuration it is possible to prevent the resin layer covering the device from being thinned and hence to improve the strength of the resin buried device.
In the device transfer method, preferably, the electrodes are each formed with their planar dimension substantially corresponding to a planar dimension of each of the resin buried devices, and the resin layer is cut by laser beams with the electrodes taken as a mask, to obtain the resin buried devices. With this configuration, it is possible to eliminate the need of use of a laser system having a high accurate positioning function and hence to reduce the production cost of the devices.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures.